Access anomaly of emergency traffic in CSMA/CA of IEEE 802.15.6

This paper focuses on the traffic prioritization in standard IEEE 802.15.6 for Wireless Body Area Network (WBAN), which is one of the emerging solutions available for the so-called wearable Internet i.e. wireless connection between electronic devices worn on or implanted in the human body. The main contribution of this work is to address the anomaly in the medium access under contention algorithms in standard 802.15.6, describe the condition in which the access anomaly may occur and propose measures to avoid it. This access anomaly can affect uplink traffic of highest data priority, so-called Emergency traffic. Due to potential applications in the field of monitoring of health variables, the priority treatment of Emergency messages must be preserved at all times. In analysing the features of the CSMA/CA scheme of the 802.15.6 protocol in a simulation model, we have found that a certain sequence of packets can bring a station into the state in which it sends highest-priority data frames with the parameters of the back-off algorithm used for traffic with a significantly lower priority. This anomaly reduces the station´s chances to access the medium under certain conditions and we provide thorough analysis of the conditions under which it can appear in the CSMA/CA algorithm of the 802.15.6 standard. Several solutions are offered in order to avoid or mitigate the affects of anomaly including the minor change to the algorithm at the level of the standard.